This invention relates to a method of accurately sensing diastolic and systolic motion of a heart, an intra-aortic balloon appartus for inflating and deflating a balloon introduced into the aorta in the vicinity of the heart, and a method of disposing the balloon apparatus at the proper intra-aortic position.
It is well-known in the art, as described in, for example the specification of U.S. Pat. No. 4,362,150. to provide cardiac assistance by introducing a balloon into the thoracic aorta of a patient and causing the balloon to inflate and deflate in accordance with the motion of the patient's heart. A balloon of this type is made to inflate during diastole and deflate during systole. This reduces the load on the left ventricle and raises aortic pressure to increase the blood flow to the coronary and carotid arterics. It is therefore essential that cardiac motion be sensed accurately to enable the balloon to be inflated and deflated correctly in accordance with the cardiac cycle.
Methods of sensing cardiac motion include measurement of aortic pressure and measurement based on an electrocardiographic signal. It has been attempted to combine means for effecting such measurements with the aforementioned intra-aortic balloon apparatus. One example in which an intra-aortic balloon is manipulated while aortic pressure is measured is disclosed in the specification of U.S. Pat. No. 4,077,394, which teaches to inflate the balloon for a prescribed period of time that begins at the occurrence of the dicrotic notch. However, since the disclosed method requires that the aortic blood be withdrawn from the patient through a central tube that passes through the balloon in order that the pressure of the blood may be measured extracorporeally, there is a time delay between actual motion of the patient's heart and a measured value showing the actual motion thereof. Moreover, though the balloon is inflated at the dicrotic notch, the occurrence of the dicrotic notch must first be verified. Owing to the time delay, however, verification of the dicrotic notch lags behinds actual occurrence, with the result that there is a tendency for the balloon to be inflated later than actually required. Additionally, the measured pressure is distorted due to the presence of the long tube, and has motion artifact added to it, both of which made consistent detection of the dicrotic notch difficult. A method of inflating and deflating the balloon based on an ECG signal is set forth in the specification of U.S. Pat. No. 3,707,960. Here two electrodes are arranged at either end of the balloon, the electrodes sense the ECG signal, and the balloon is inflated and deflated in dependence upon a R-wave contained in the signal. The problem with this method is that in some patients the balloon should be deflated prior to the detection of the R-wave thus necessitating prediction of its occurence.
Other shortcoming common to the prior art include problems in correctly disposing the balloon within the thoracic aorta.